This invention relates to a fuel injection system for multi-cylinder internal combustion engines, and more particularly to a fuel injection system of this kind which is adapted to utilize the residual fuel pressure present in the injection pipes at the termination of each fuel injection for the immediately following fuel injection.
In fuel injection systems for diesel engines or the like, injecting fuel should be atomized to the finest possible particle size in order to achieve complete combustion of a required quantity of fuel in an engine cylinder in the shortest possible time. To this end, in recent years more and more attempts have been made to enhance the injection pressure of fuel injection systems of this kind. Particularly fuel injection systems for direct-injection engines are required to achieve very high injection pressure of 600 Kg/cm.sup.2 for instance. On the other hand, in conventional fuel injection systems, in order to obtain sharp cut-off of fuel injection at the end of each fuel injection the fuel pressure in the injection pipe is reduced to a value almost equal to atmospheric pressure due to the retraction stroke of the delivery valve, and at the next fuel injection the same fuel pressure is raised up to a required value from the value almost equal to atmospheric pressure. In a conventional fuel injection pump, a camshaft, which is rotated in unison with the rotation of the engine to reciprocate the plungers of the pump, has its cam profile designed so as to obtain a rise in the fuel pressure in the injection pipe from atmospheric pressure or like pressure to required injection pressure during each fuel injection. However, it is difficult to increase the effective stroke length of the plungers beyond a certain value by changing the cam profile, making it difficult to obtain higher injection pressure.